Yes, they are compatible. But. You would do yourself a =very= great service to keep them -both- installed. There are some very different ways that P5 handles things, such as the material shaders, that has a learning and tedium curve. You can set up a figure in P4, save it as a pz3, then open it in P5 and see how things are interpreted. Plus you have the option of simply linking your current runtime into P5 without reinstalling a thing (Bliss......).